Especially in oil wells which pump high viscosity, tarry crude, there is a decided tendency for paraffin to adhere to the internal wall of the well liner, and for material such as particulates to clog the perforations in the liner. As a consequence, well production decreases markedly, and it is necessary from time to time to stimulate the well by removing this deleterious material. This process is called "washing" the well. In the course of this process, some of the material may be forced into the formation. This process has the further advantage that it may assist in "breaking" the formation which will open it up to increased flow toward the well.
It is known to use brushes and knives, lowered into the well, to do this work, but in the known prior art, they are fully extended and in contact with the wall of the lines from the time the tool is first lowered into the well. As a consequence, these tool parts, which are subjected to very hard wear, are often nearly worn out before they reach the region intended to be treated, namely the region at and near the perforations. A less efficient treatment is then to be expected. In addition, the tool must be reconditioned more frequently because of the additional wear and the well casing is also subjected to needless wear.
It is an object of this invention to provide a wash tool which carries brushes, or blades, or both as working components in which the working components are not brought into working contact with the well liner until the tool reaches the depth at which the stimulation treatment is to be effected. As a consequence, a new and fresh (or newer and fresher) set of working components works on the selected region, the time between reconditioning is extended, and unnecessary casing wear is averted.